The present invention is directed, in general, to transfer molding during integrated circuit packaging and, more specifically, to transfer molding tolerating localized lead frame or packaging substrate thickness variations.
Conventional transfer molding systems employed for integrated circuit packaging generally utilize hardened steel mold surfaces to clamp onto the lead frame or packaging substrate, forming the mold cavity as shown in FIG. 4. Mold system 400 includes a lower mold portion 401 and an upper mold portion 402 receiving an integrated circuit die 403 affixed to a packaging substrate 404 by an adhesive, electrically connected by wire bonds to conductive traces on the packaging substrate.
The lower mold portion 401 has an upper surface that contacts the bottom surface of packaging substrate 404 while the upper mold portion 402 defines a cavity 405 around integrated circuit die 403, the wire bonds and a portion of the upper surface of packaging substrate 404, contacting the upper surface of the packaging substrate 404 only around a periphery of the cavity 405. Once the mold portions 401 and 402 are assembled with an integrated circuit die 403 and packaging substrate 404 received therein as shown in FIG. 4, encapsulating material such as epoxy or thermosetting resin is injected into the cavity 405, forming the packaged integrated circuit.
Such transfer molding systems, however, are poorly suited where the lead frame or packaging substrate has local thickness variations. Either leakage of the encapsulating material or damage to the packaging substrate 404 (e.g., damage to the conductive traces thereon) may result.
When the integrated circuit die being packaged requires an exposed active area after packaging (e.g., for capacitive or light sensors therein), similar problems arise. As illustrated in FIG. 5, the mold system 500 for packaging exposed active area integrated circuits typically includes lower and upper mold portions 501 and 502, respectively, receiving an integrated circuit die 503 mounted on a packaging substrate 504. Upper mold 502 defines a cavity 505 around integrated circuit die 503 and a portion of packaging substrate 504, with a portion of the upper mold 502 contacting the active area 506 to prevent injected encapsulating material from contacting that surface, leaving the active area 506 exposed after packaging.
When packaging exposed active area integrated circuits utilizing a mold system of this type, non-uniformity or non-planarity of the adhesive employed to affix the integrated circuit die (exaggerated in FIG. 5) can cause imperfect contact of the upper mold with the active area, resulting of leakage of the encapsulating material onto the active area or damage to the integrated circuit die active area.
There is, therefore, a need in the art for a transfer molding system tolerating thickness variations in the lead frame or packaging substrate, and additionally tolerating non-planarity of the integrated circuit die for circuits requiring exposed active areas after packaging.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide, for use in transfer molding system, a bottom mold portion that is covered with a deformable material. During mold clamping, the deformable material contacts the bottom surface of the packaging substrate on which the integrated circuit die is mounted. Deformation of this relatively soft covering on the bottom mold portion accommodates thickness variations in the packaging substrate, as well as non-planarity of the adhesive layer between the integrated circuit die and packaging substrate in exposed active area integrated circuits.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, it may be advantageous to set forth definitions of certain words or phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9corxe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, whether such a device is implemented in hardware, firmware, software or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases.